This invention relates to an apparatus for stabilizing the light output of a high pressure discharge lamp which generates a highly stable light output when used as a light source in an apparatus for performing spectrochemical analysis, for example, an absorption photometer.
Light used in the field of spectrochemical analysis occupies a wide wavelength range of from the ultraviolet range to the visible range of the spectrum. Especially, in an apparatus used for qualitative and quantitative analysis of a substance by absorption, among various apparatus designed for performing spectrochemical analysis, it is very important for its light source to be able to generate a light output which is substantially free from fluctuation. However, even in a metal halide lamp especially developed for the purpose of minimizing fluctuation of its light output, it is difficult to decrease fluctuation of the light output to less than 0.05%. In a high vapor pressure discharge lamp commonly used for illumination purpose, such as, a high pressure mercury lamp, a high pressure sodium lamp, a metal halide lamp or the like in which the vapor pressure during operation is about 1 atm or more, fluctuation of about 0.5% occurs commonly in its light output, and light output fluctuation of about several percent occurs when the arc snakes.
Methods for preventing snaking of the arc in such a lamp by imparting a magnetic force to the arc have already been proposed, as disclosed in Japanese Utility Model Publication No. 49-5112 (filed by Mitsubishi Electric Corporation on Mar. 17, 1969) and U.S. Pat. No. 3,562,583 filed on Jan. 27, 1969 by Robert J. Zollweg et al. The proposed methods have been effective for preventing the illumination light output of such a lamp from flickering and for preventing determination of the lamp performance due to bowing of the arc, thereby ensuring good life performance of the lamp. However, the proposed methods have not been sufficient to meet the demand for highly stabilizing the light output, that is, decreasing the fluctuation of the light output to less than 0.05%.
As pointed out above, the prior art high pressure discharge lamp has been insufficient in the stability of its light output and has not been suitable for use as a light source of a spectrochemical analyzing apparatus such as an absorption photometer in which the light source is required to generate a highly stable light output.